The extractor disclosed in the '622 patent comprises an elongated cannula assembly having an annularly expanding and retracting gripping and releasing mechanism at the distal end thereof and a moving assembly at the proximal end thereof. The gripping and releasing mechanism includes an annular series of longitudinally fixed flexure elements and a corresponding series of longitudinally movable flexure elements. The moving assembly is operable to effect a relative movement between the flexure elements to move them between a retracted condition and an expanded condition defined by an annular series of transversely outwardly flexed fixed elements interconnected by an annular series of arcuately flexed portions of said flexure elements.
While the disclosed configurations of the '622 patent when made with relatively large dimensions are satisfactory, difficulties occur in attempting to miniaturize the disclosed constructions into a three French size such as required by many popular scopes. These size restrictions create an especially troublesome problem in providing a cost effective construction and method for making the gripping and releasing mechanism embodied in a medical device suitable for both extracting stones directly from the kidneys as well as extracting stones from the ureter. This is because of the chamber configuration of the kidneys, which make the usual closed pointed end of a urethral basket, which operates in the elongated tubular configuration of the ureter, inappropriate. Moreover, it is necessary to negotiate a severe turn to get to the kidney chambers. The heart of the problem lies in the construction and method used to accomplish the connection between each movable flexure element and the distal end of a corresponding fixed flexure element. Several different arrangements are disclosed in the above cited patent, but none have appeared on the commercial market. There exists a need to provide a commercially acceptable cost effective construction and method for forming a gripping and releasing mechanism of the type described which solves the identified problem.